Plasma endogenous opioids and dexamethasone suppression test in depression

The role of beta-endorphin in the pathophysiology of major depression

A role for beta-endorphin (beta-END) in the pathophysiology of major depressive disorder (MDD) is suggested by both animal research and studies examining clinical populations. The major etiological theories of depression include brain regions and neural systems that interact with opioid systems and beta-END. Recent preclinical data have demonstrated multiple roles for beta-END in the regulation of complex homeostatic and behavioural processes that are affected during a depressive episode. Additionally, beta-END inputs to regulatory pathways involving feeding behaviours, motivation, and specific types of motor activity have important implications in defining the biological foundations for specific depressive symptoms. Early research linking beta-END to MDD did so in the context of the hypothalamic-pituitary-adrenal (HPA) axis activity, where it was suggested that HPA axis dysregulation may account for depressive symptoms in some individuals. The primary aims of this paper are to use both preclinical and clinical research (a) to critically review data that explores potential roles for beta-END in the pathophysiology of MDD and (b) to highlight gaps in the literature that limit further development of etiological theories of depression and testable hypotheses. In addition to examining methodological and theoretical challenges of past clinical studies, we summarize studies that have investigated basal beta-END levels in MDD and that have used challenge tests to examine beta-END responses to a variety of experimental paradigms. A brief description of the synthesis, location in the CNS and behavioural pharmacology of this neuropeptide is also provided to frame this discussion. Given the lack of clinical improvement observed with currently available antidepressants in a significant proportion of depressed individuals, it is imperative that novel mechanisms be investigated for antidepressant potential. We conclude that the renewed interest in elucidating the role of beta-END in the pathophysiology of MDD must be paralleled by consensus building within the research community around the heterogeneity inherent in mood disorders, standardization of experimental protocols, improved discrimination of POMC products in analytical techniques and consistent attention paid to important confounds like age and gender.

Inhibition of the pituitary-adrenal axis with dexamethasone and cortisol in depressed patients and healthy subjects: a dose-response study

Different doses dexamethasone (0.25, 0.5, and 1 mg) or cortisol (30, 60, and 120 mg) were administered PO at 2230h to 39 depressed patients and 20 healthy subjects on nonsuccessive days. The inhibiting capacity of the two steroids on hypothalamo-pituitary axis (HPA) function was evaluated by measuring the plasma levels of cortisol, ACTH, and beta-endorphin at 0900h and 1530h each day following treatment. Baseline levels of the hormones were measured before starting treatment. A dose-dependent suppressive effect of both steroids on the plasma levels of cortisol, ACTH, and beta-endorphin was found both in patients and controls, except for the 0900h levels of cortisol after cortisol treatment. The effects were most profound in the morning. Differences between patients and controls were observed after cortisol treatment, but not dexamethasone, with respect to cortisol, ACTH, and beta-endorphin plasma levels in the morning. Cortisol treatment discriminated dexamethasone nonsuppressors from suppressors (patients and controls) and patients categorized as dexamethasone suppressors from controls in a way that dexamethasone treatment could not. The data favour the idea of impaired corticosteroid feedback beyond the pituitary level as part of HPA dysfunction.

Beta-endorphin responses to metyrapone and dexamethasone in depressed patients

Controversy continues over the characteristics of beta-endorphin secretion in depression. Beta-endorphin plasma levels were measured in 30 drug-free male patients with a DSM-III-R major depressive disorder and 21 healthy controls. Depressed patients displayed significantly lower beta-endorphin plasma levels in baseline conditions, after the single dose metyrapone test, and after the dexamethasone suppression test. The activation of hypothalamic-pituitary-adrenal (HPA) axis in depression might be due, at least in part, to low levels of beta-endorphin. These results suggest that HPA axis dysregulation in depression may involve peptides other than ACTH.

Stimulation of the pituitary-adrenal axis with a low dose [Arg8]-vasopressin in depressed patients and healthy subjects

Graded doses arginine-vasopressin (AVP) were administered to depressed patients and control subjects to compare the sensitivity of the pituitary-adrenal system of these subjects for this compound. The plasma levels of cortisol, adrenocorticotropic hormone (ACTH) and beta-endorphin were measured before and after intravenous AVP injection. The hormonal output was taken as a measure of pituitary-adrenal function. In control subjects 3 doses AVP and placebo were used, whereas in patients two doses AVP, a low and a high dose, and placebo were tested. All tests were carried out in the afternoon when the pituitary-adrenal system is stable and more susceptible for stimulation. Patients were subdivided into dexamethasone suppressors and nonsuppressors based on their DST status before testing to look for differences among these groups. Control subjects showed no response of the hormones to the lowest dose AVP and a moderate response to the higher doses. Interestingly, depressed patients as compared to controls responded more to the lowest dose AVP in particular with respect to ACTH. DST status did not influence the results. These findings suggest an enhanced sensitivity of the pituitary to low doses AVP in depressed patients. Thus, AVP might play a role in HPA dysfunction in depression.

Abnormal pituitary function during melancholia: reduced alpha-melanocyte-stimulating hormone secretion and increased intact ACTH non-suppression

In order to investigate pituitary alpha-melanocyte-stimulating hormone (alpha-MSH), intact (1-39 structure) adrenocorticotropic hormone (ACTH), and adrenal cortisol secretion, we measured 8 a.m. plasma levels of those hormones before and after administration of 1 mg dexamethasone in 39 depressed inpatients and 10 healthy controls. We found a significantly lower baseline alpha-MSH secretion in melancholic patients as opposed to healthy controls. There were no significant relations between alpha-MSH secretion on the one hand and ACTH or cortisol secretion on the other. Dexamethasone did not affect the 8 a.m. alpha-MSH circulating levels. The post-dexamethasone intact ACTH and cortisol values were significantly higher in melancholics as compared with healthy, minor and simple major depressed subjects. ACTH non-suppression was defined as post-dexamethasone intact ACTH greater than or equal to 12 pg/ml. ACTH non-suppression was found to be more sensitive (70%) and specific (100%) for melancholia than cortisol non-suppression. By means of pathway analysis we have established that cortisol non-suppression during a severe depression is completely determined by an augmented ACTH escape from suppression by dexamethasone. It is concluded that the assay of post-dexamethasone intact ACTH could, in the future, replace post-dexamethasone cortisol determination.

A multivariate study of simultaneous escape from suppression by dexamethasone of urinary free cortisol, plasma cortisol, adrenocorticotropic hormone and beta-endorphin in melancholic patients

To investigate the relationships between pre- and postdexamethasone hypothalamic-pituitary-adrenal (HPA) axis functioning in depression, we measured the levels of baseline and postdexamethasone urinary free cortisol (UFC), plasma cortisol, adrenocorticotropic hormone (ACTH) and beta-endorphin. We found that dexamethasone significantly suppressed all hormone levels. All 4 postdexamethasone hormones--but not their baseline levels--were significantly higher in melancholic subjects than in minor and simple major depressives. We have accumulated evidence that the melancholic and minor depression groups form discrete classes in postdexamethasone HPA axis hormone levels; this supports the biological heterogeneity hypothesis of melancholia. We found that a combination of the postdexamethasone UFC and beta-endorphin values yielded the most significant diagnostic tool for melancholia. Our results suggest that the measurements of both hormones may constitute the most accurate index reflecting the HPA axis escape from suppression by dexamethasone in melancholia. By means of pathway analysis, we determined the causal relationships between age, dexamethasone circulating levels, diagnostic depression classification and the various baseline and postdexamethasone hormone values.

An augmented escape of beta-endorphins to suppression by dexamethasone in severely depressed patients

Baseline beta-endorphin and cortisol levels and their responses to 1 mg dexamethasone were measured in 11 healthy controls and in 35 depressed patients, categorized according to the DSM-III. Dexamethasone significantly suppressed beta-endorphin levels. Depressed patients with melancholia/psychotic features exhibited significantly increased post-dexamethasone beta-endorphin levels compared with healthy controls, minor and simple major depressives; the baseline beta-endorphin levels did not differ between those study samples. Post-dexamethasone beta-endorphin and cortisol values were found to be significantly and positively correlated. Accordingly, cortisol non-suppressors showed significantly higher post-dexamethasone beta-endorphin levels. Post-dexamethasone beta-endorphin may be the most sensitive and specific reflection of the disorder in negative feedback exerted by dexamethasone in depression.

Psychoneuroendocrine research in depression. I. Hormone levels of different neuroendocrine axes and the dexamethasone suppression test

Psychoneuroendocrinology is of major importance in the biological research of depression. Most studies have focussed on the regulation of the hypothalamic-pituitary-adrenal (HPA) axis but other endocrine systems such as the hypothalamic-pituitary-thyroid (HPT), hypothalamic-pituitary-somatotropic (HPS), and the hypothalamic-pituitary-gonadal (HPG) axis have also been shown to be involved in the psychobiology of depression. There are close interrelations between various endocrine axes which possibly are affected during depressive illness. A variety of neuroendocrine abnormalities has been detected in depressive disorder but the pathophysiology of these derangements remains still unclear. Although the currently used neuroendocrine tests are not of diagnostic validity they may help to clarify the pathophysiological significance of the complex regulatory mechanisms of different neuroendocrine axes in affective disorders. Neuroendocrine regulation is determined both by peripheral and central mechanisms which both have to be adequately considered as well as potent interactions between various endocrine systems in further neuroendocrine depression research.

Clinical relevance of endorphins in psychiatry

1. 13 years after the discovery of endorphins, the relationships between these peptides and mental illness remain unclear. 2. Current concepts are controversial and convincing hypotheses have not been elaborated yet. 3. Endorphin measurements in CSF or serum of psychiatric patients did not strongly support that schizophrenia or depression is related to a deficit or an excess of these peptides. Moreover, treatment with endorphins or opiate antagonists did not result in a distinct change of psychiatric symptoms. Recently, research focused on the relationship between endorphins and addictive behavior, but substantial evidence for clinical relevance is still missing. 4. The physiological relevance of many newly discovered endorphins is barely known and several subtypes of the opiate receptor have been found. Thus, it will still require a substantial effort in basic and clinical studies before, if at all, endorphins turn out to be helpful in the treatment of mental illness.